This invention concerns secondary recovery in petroleum producing, in general. More specifically, it relates to a method that applies to secondary recovery where an injection well is employed and wherein the fluid injected into the formation withdraws back into the injection well. Such conditions have been found to cause a heavy residue that fills the pores of the surrounding formation and any gravel pack that is being used. Furthermore, while the application of steam could easily dissolve normally occurring deposits of mere paraffin, the heavy residue has been discovered to be intractable to such treatment. However, a method according to this invention frees the foregoing heavy residue from the porous formation, so that an injection procedure may proceed unimpeded.